As Ratchet Bomb’s last ability resolves, its last existence on the battlefield is checked to determine how many charge counters were on it.

1/1/2011

Ratchet Bomb’s second ability destroys only those nonland permanents whose converted mana cost is exactly equal to the number of charge counters on Ratchet Bomb. It doesn’t matter who controls them.

1/1/2011

If Ratchet Bomb’s second ability is activated while it has no charge counters on it, it will destroy each nonland permanent with converted mana cost 0.

1/1/2011

The converted mana cost of a permanent is determined solely by the mana symbols printed in its upper right corner, unless it’s copying something else (see below). The converted mana cost is the total amount of mana in that cost, regardless of color. For example, a card with mana cost has converted mana cost 5.

1/1/2011

If a permanent is copying something else, its converted mana cost is the converted mana cost of whatever it’s copying.

1/1/2011

In all cases, ignore any alternative costs or additional costs (such as kicker) paid when the permanent was cast.

1/1/2011

If the mana cost of a permanent includes , X is considered to be 0.

1/1/2011

If a nonland permanent has no mana symbols in its upper right corner (because it’s a token that’s not copying something else, for example), its converted mana cost is 0.